Sliding member

ABSTRACT

Provided is a sliding member which has high seizure resistance though an overlay layer comprising Ag as the main component is used therein. The sliding member of an embodiment comprises a base and an overlay layer which is disposed on the sliding-side surface of the base and which comprises Ag as the main component and contains Al. The overlay layer comprising Ag as the main component is relatively soft. Due to this, the overlay layer comprising Ag as the main component can ensure high seizure resistance even when the use of Pb is avoided. Furthermore, the overlay layer comprising Ag as the main component has excellent thermal conductivity. Due to this, frictional heat generating at the sliding part rapidly dissipates to the base side.

TECHNICAL FIELD

The present invention relates to a sliding member.

BACKGROUND ART

Conventionally, a sliding member of a slide bearing for an internal-combustion engine etc. comprises an overlay layer on a sliding-side surface of a base such as a steel back plate. For such an overlay layer, there is proposed an overlay layer which comprises Ag as a main component and to which In, Sn, Bi, or the like is added, in order to obtain sliding characteristics to the same degree as those of a sliding member containing Pb, while avoiding the use of Pb (Patent Literature 1).

However, although In, Sn, and Bi are softer than Ag, their thermal conductivities are extremely smaller than that of Ag. Therefore, an overlay layer which comprises Ag as a main component and to which In, Sn, or Bi is added cannot easily dissipate the heat generated in the sliding part with a mating member, to the base side. As a result, the temperature of an overlay layer of this type easily rises under severer conditions, causing reduction in strength and hardness, which causes a problem of easily resulting in seizure.

CITATION LIST Patent Literature

PATENT LITERATURE 1: JP-A-11-257355

SUMMARY OF INVENTION Technical Problem

Therefore, an object of the present invention is to provide a sliding member having high seizure resistance even when an Ag-based overlay layer is used.

Solution to Problem

The sliding member according to claim 1 comprises: a base; and an Ag-based overlay layer disposed on a sliding-side surface of the base and comprising Al.

Moreover, the sliding member according to claim 2 comprises: a base; and an Ag-based overlay layer disposed on a sliding-side surface of the base and comprising Al, the overlay layer further comprising at least one of Sn and Zn.

The Ag-based overlay layer is relatively soft. Therefore, the Ag-based overlay layer can ensure high seizure resistance even when the use of Pb is avoided. Moreover, the overlay layer comprising Ag has excellent thermal conductivity. Therefore, the frictional heat generated at a sliding part is rapidly dissipated to the base side. The present inventors have found that the addition of Al to an Ag-based overlay layer does not cause significant reduction in the thermal conductivity of the overlay layer. That is, the addition of In, Sn, Bi, or the like to an Ag-based overlay layer has been known as a prior art. However, In, Sn, and Bi as additive elements have small thermal conductivity, and they have a problem of disturbing rapid dissipation to the base side of the heat generated in the sliding part with a mating member. On the other hand, Al in the present invention has a relatively large thermal conductivity and facilitates the function of an Ag-based overlay layer, that is, rapid heat dissipation to the base side by the high thermal conductivity. Therefore, the sliding member of the present invention can achieve high seizure resistance even when an Ag-based overlay layer is used, and it can endure even in the use under severer conditions.

Moreover, the Ag-based overlay layer of the present invention may comprise not only Al but also at least one of Sn and Zn as an additive element. Thus, the essence of the present invention is in that an Ag-based overlay layer comprising Al is provided. Therefore, the present invention does not eliminate that an additive element other than Al and unavoidable impurities are contained in the overlay layer.

In the sliding member according to claim 3, the overlay layer comprises 0.1% by mass to 15% by mass of Al. In the Ag-based overlay layer, the original thermal conductivity of Ag is exhibited as the proportion of Ag increases, and the heat dissipation from the overlay layer to the base side is facilitated. On the other hand, as the proportion of Al contained in the overlay layer increases, the thermal conductivity of the overlay layer comes close to the thermal conductivity of Al from the original thermal conductivity of Ag. Thus, in the present invention, when adding Al to an overlay layer, the upper limit of Al is 15% by mass.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view of a sliding member according to an embodiment.

FIG. 2 is a schematic view showing the test results of a sliding member according to an embodiment.

FIG. 3 is a schematic view showing the conditions of the seizure resistance test of a sliding member according to an embodiment.

FIG. 4 is a schematic view showing a sample used for the seizure resistance test of a sliding member according to an embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a specific embodiment of a sliding member will be described.

First, the procedures for producing a sliding member to be used as a sample in the present embodiment will be described.

As shown in FIG. 1, a sliding member 10 comprises a base 11 and an overlay layer 12. The base 11 has a back plate layer 13 and a Cu-based or Al-based bearing alloy layer 14. The back plate layer 13 is formed from steel. Thus, the base 11 is a so-called bimetal comprising the steel back plate layer 13 and the Cu-based or Al-based bearing alloy layer 14. The base 11 formed from the back plate layer 13 and the bearing alloy layer 14 is shaped into a semicylindrical or cylindrical shape. The surface of the shaped base 11 on the side of the bearing alloy layer 14 is subjected to surface machining such as boring. The surface of the base 11 subjected to surface machining is washed by electrolytic degreasing and with acid. Thus, after the surface of the base 11 is washed, an Ag-based overlay layer 12 made of an Ag—Al alloy is formed thereon by sputtering or the like. Further, instead of sputtering, the overlay layer 12 can also be formed by plating Ag on a layer made of Al and by forming an Ag—Al alloy comprising Ag as a main component utilizing diffusion. In this case, the diffusing capacity and distribution of Al in the overlay layer 12 can be controlled by temperature and time. Moreover, one or two or more intermediate layers (not shown) may be disposed between the base 11 and the overlay layers 12.

In the present embodiment, the overlay layer 12 is formed by sputtering using a magnetron sputtering system (not shown). A specific example for forming the overlay layer 12 will be described using the sliding member 10 of sample 1, which is an Example shown in FIG. 2. In the case of sample 1, a base 11 after washing consisting of bimetal is mounted on a base mounting part of a magnetron sputtering system. Moreover, Ag and Al serving as the materials for the overlay layer 12 are mounted on a target mounting part of the magnetron sputtering system as targets.

After the base 11 and Ag and Al which are the targets are mounted, the chamber of the magnetron sputtering system is decompressed to 1.0×10⁻⁶ Torr and adjusted to 2.0×10⁻³ Torr by supplying Ar gas. After the pressure of the chamber is adjusted, the surface of the base 11 is cleaned with Ar gas. In this case, a bias voltage of 1000 V is applied to the surface of the base 11. This produces Ar plasma between the base 11 and Ag and Al serving as targets, and reverse sputtering is performed for 15 minutes. After the cleaning with Ar plasma is performed, voltage is applied to each target so that a current of 8 A to 14 A may flow into Ag as a target and a current of 0.5 A to 6 A may flow into Al as a target. At this time, the bias voltage between the base 11 and the targets is set between 100 V and 200 V. According to these procedures, Ag and Al serving as targets are sputtered by the collision of Ar ions and form a film on the surface on the side of the bearing alloy layer 14 of the base 11.

When a produced sample corresponding to sample 1 was subjected to EPMA (Electron Probe Micro Analysis), it was verified that Al was uniformly dispersed in the overlay layer 12 with Ag being used as a matrix. The amount of Al added to the Ag-based overlay layer 12 can be controlled by adjusting the mass ratio of Ag and Al to be mounted on a target mounting part as the targets of sputtering and the current to be passed through the Ag and Al serving as targets.

Sliding members 10 of samples 1 to 16 corresponding to Examples and sliding members 10 of samples 17 to 20 corresponding to Comparative Examples as shown in FIG. 2 were formed according to the above procedures.

(Seizure Resistance Test)

The resulting sliding members 10 of samples 1 to 16 as Examples and samples 17 to 20 as Comparative Examples were verified for seizure resistance by a shim biting test.

The test conditions of the shim biting test are shown in FIG. 3. In the shim biting test, a test sample is prepared by attaching a metal shim 15 having a size of 2 mm×2 mm×t to the outer circumferential surface of each of the sliding members 10 of samples 1 to 16 as Examples and samples 17 to 20 as Comparative Examples, as shown in FIG. 4. In the test, the thickness t of the shim 15 is set to 10 μm. The thickness t of the shim 15 can be set from about 10 μm to 30 μm depending on the conditions of the test. The test sample of the sliding member 10 is installed in a rotational load tester which is a seizure tester (not shown). The shim 15 is attached to the test sample of the sliding member 10. Thus, when the test sample of the sliding member 10 is installed in the seizure tester, a portion corresponding to the shim 15 on the test sample of the sliding member 10 projects to the inner circumferential side depending on the thickness of the shim 15. This projected portion generates heat by contacting with the test shaft of the seizure tester. Therefore, the amount of heat generated by the contact of the test sample of the sliding member 10 with the test shaft is increased by increasing the load applied to the test sample of the sliding member 10 in contact with the test shaft. As a result, the lower the thermal conductivity of the overlay layer 12 in the test sample of the sliding member 10 is, the more easily seizure will be occurred on the overlay layer 12 at an early stage. In the test in the present embodiment, the load applied to the test sample of the sliding member 10 is increased by 5 MPa every 10 minutes. Then, when the back temperature of the test sample of the sliding member 10 exceeds 200° C., or when a slide occurs in a shaft drive belt of the seizure tester by the variation of torque applied to the seizure tester, it is determined that seizure has been occurred in the test sample of the sliding member 10.

Hereinafter, concerning the seizure resistance, verification results will be examined based on FIG. 2 from the viewpoint of the maximum specific load without seizure (MPa).

Samples 1 to 16 are Examples in which Al is added to the Ag-based overlay layer 12. The seizure resistances of these Examples have improved as compared with samples 17 to 20 as Comparative Examples. That is, samples 1 to 16 as Examples have better seizure resistance by adding Al to the Ag-based overlay layer 12 than sample 17 in which the overlay layer 12 comprises only Ag. This is probably because conformability is improved by adding Al that is softer than Ag, thereby improving seizure resistance. Similarly, samples 1 to 16 as Examples have better seizure resistance than sample 18 in which Sn is added to the Ag-based overlay layer 12 without adding Al, sample 19 in which In is added similarly, and sample 20 in which Bi is added similarly. The seizure resistances of samples 1 to 16 have been improved probably because the thermal conductivity of the overlay layer thereof is larger than that of samples 18, 19, and 20.

On the other hand, although the seizure resistances of samples 15 and 16 as Examples are higher than that of sample 17 as a Comparative Example, it is lower than that of sample 14 as an Example. This shows that, in the Ag-based overlay layer 12, an increase in the amount of Al added tends to reduce the seizure resistance. That is, when the amount of Al added to the Ag-based overlay layer 12 becomes excessive, the thermal conductivity of the overlay layer 12 will be closer to that of Al than Ag. Therefore, it is considered that samples 15 and 16 in which the amount of Al added is high have lower seizure resistance than sample 14. Consequently, it has been found that the addition of Al to the overlay layer 12 achieves improvement in seizure resistance, and the addition of a predetermined amount of Al contributes to the exertion of excellent seizure resistance.

Moreover, the seizure resistance of sample 5 as an Example is better than that of sample 4, and the seizure resistance of sample 8 is better than that of sample 9. Similarly, the seizure resistance of sample 11 is better than that of samples 12 and 13. This shows that, in the case of the Ag-based overlay layer 12 comprising Al, when the content of Al is approximately the same, the seizure resistance can be more improved by not adding Sn, Cu, Zn, or Bi. That is, when an element having a smaller thermal conductivity than Al is added to the Ag-based overlay layer 12, the thermal conductivity of the overlay layer 12 will be smaller than the case where only Al is added. Therefore, it is considered that samples 4, 9, 12, and 13 in which an element other than Al is added to the overlay layer 12 have a lower seizure resistance than a sample in which substantially only Al is added and the content of Al in the overlay layer 12 is about the same. Consequently, it has been found that although seizure resistance can be ensured even if an element other than Al is added to the overlay layer 12, the addition of an element other than Al is not advantageous to seizure resistance.

Moreover, it has been found that, based on samples 1 to 16 as Examples, the presence or absence of an intermediate layer, the type of an intermediate layer, and the type of the bearing alloy layer 14 have only a small influence on seizure resistance. Furthermore, although not particularly shown, it has been found that, even if Al is added to the Ag-based overlay layer 12, and, in addition, hard particles and metal elements other than those shown in Examples are added thereto, a higher seizure resistance than that of the overlay layer 12 comprising only Ag can be achieved. Consequently, if Al is added to the Ag-based overlay layer 12, an improvement in seizure resistance can be achieved regardless of the presence or absence of other additive components or the type of additive components, as long as the amount of Al added is not excessive.

Moreover, in the sliding member 10, other layers such as a conformable layer may further be disposed on the sliding-side surface of the Ag-based overlay layer 12. A further layer such as a conformable layer is preferably a layer comprising, for example, Bi or a Bi alloy. Although not particularly shown, a sliding member of an embodiment in which a conformable layer is disposed also has excellent seizure resistance and, in particular, had excellent initial conformability. Thus, the sliding member 10 of an embodiment in which a conformable layer is disposed was naturally able to exhibit high seizure resistance even if the conformable layer was worn out to expose the Ag-based overlay layer 12.

The present invention as described above is not limited to the above embodiments and can be applied to various embodiments without departing from the scope of the present invention.

REFERENCE SIGNS LIST

-   10 Sliding member -   11 Base -   12 Overlay layer -   13 Back plate layer -   14 Bearing alloy layer 

1. A sliding member comprising: a base; and an Ag-based overlay layer disposed on a sliding-side surface of the base and comprising Al.
 2. A sliding member comprising: a base; and an Ag-based overlay layer disposed on a sliding-side surface of the base and comprising Al, the overlay layer further comprising at least one of Sn and Zn.
 3. The sliding member according to claim 1, wherein the overlay layer comprises 0.1% by mass to 15% by mass of Al.
 4. The sliding member according to claim 2, wherein the overlay layer comprises 0.1% by mass to 15% by mass of Al. 